This is very neat. I wonder what the energy loss is, between what's required to lift the water and what's gained by releasing it. Regardless, eco-friendly high density "batteries" are a great concept.
It's probably very low efficiency, but if you can design renewable energy systems to provide enough overage during peak generation periods, maybe it doesn't matter.
As an example, MKBHD's solar roof produces something like 30KW during peak sunlight, which is so much more than his home uses (even with air conditioning turned on) that it can charge his house batteries to 100% and gives him power to sell back to the electric company for future power credits.
Admittedly, not everybody has a house with a large roof or $120K to spend on solar. But if we can drive solar and wind power down enough in price per unit, the efficiency of the storage system becomes a lot less of a concern.
A system like this is designed to use excess generated power during times of low demand and then to put power back into the grid during peak usage times. This can help negate the need to bring another plant online and they can probably sell the power at higher prices during peak usage.
Yeah at the end of the day renewable energy is rapidly becoming pretty close to free. Efficiency doesn't matter as much when the energy costs nothing to generate.
If you have the system always running most of the cartage back to the top could be handled by the siphoning effect, like draining a washing machine or siphoning patrol.
You'd need energy to get it started but after that it should keep siphoning as long as there's liquid to siphon.